Semiconductor radiation sources have been known for a long time. They may have light-emitting diodes or LEDs whose emission spectrum can be adapted to the requirements as regards the sensitivity spectrum of the materials to be cured by appropriately selecting the LEDs.
Light curing devices must be calibrated, as has already been disclosed, for example, in U.S. Pat. No. 6,095,812. On the other hand, the practice of calibrating light-emitting diodes, which are connected in parallel with one another, using series resistors has also already been disclosed, as regards which reference may be made, for example, to DE 100 37 420. In this solution, the LED chips are arranged in a type of matrix and the respective associated series resistors can be adjusted by means of laser trimming.
When implementing light curing devices, it is desirable to provide particularly high light emission at precise points in order to rapidly provide the through-curing in the desired quality. In this respect, it has been disclosed to combine light-emitting diodes in a closely adjacent manner and to focus the light emitted by the light-emitting diodes using suitable optical measures such as a converging lens.
On the other hand, this raises the problem of sufficient cooling especially in the case of high-power light-emitting diodes and LED chips. Sufficient cooling can, in practice, only be provided by directly applying the LED chips to a base body as a heat sink which has been intensively prepared for heat dissipation.
Nevertheless, the surroundings of the LED chips are really hot, with the result that it must also be ensured, for example, that the converging lens which usually comprises plastic is not inadvertently deformed.
Resistors frequently comprise a layer-like carrier material with graphite incorporations. The desired resistance can be set within wide ranges by selecting the thickness and other dimensions of the resistance layer; the resistance value can be selected to be of virtually any desired order of magnitude (from the m range to the T range) by selecting the mixture which is provided for the resistance track or layer.
It has already been proposed to centrally arrange the LED chips on a heat sink using dense packing and to arrange resistance layers outside this region. An attempt has been made, by laser-trimming the resistors, to bring the power of the individual LED chips more into line with one another. During operation, LED chips of this type nevertheless frequently exhibit an uneven power distribution which is unsatisfactory and could not really be eliminated even by repeated readjustment.